The long-term aim of this proposal is directed to an understanding of the structural organization of a gene in a higher eucaryote, and the relationship of that organization to the time and tissue specific control during development of the expression of that gene. The rosy locus of Drosophila melanogaster, which codes for the enzyme xanthine dehydrogenase (XDH) is our chosen model system. The experiments proposed represent a continuation of ongoing studies and make use of genetic, biochemical, immunochemical, histochemical and molecular techniques in the analysis. In addition to utilization of methods in prior work the proposal includes gradient denaturation gel mapping to localize small DNA lesions, the generation of deletions by hybrid dysgenesis and their analysis including rapid sequencing of important regions, and transformation experiments involving in vitro induced mutations and constructs.